Flash lighting operating circuit for a fluorescent discharge lamp



Sept. 29, 1959 TAKIZO KQBAYASHI FLASH LIGHTING OPERATING CIRCUIT FOR A FLUORESCENT DISCHARGE LAMP Filed April 17, 1957 1N VENTOR ATTORNEY 2,905,923 Patented Sept. 29, 1959 FLASH LIGHTING OPERATING CIRCUIT FOR A FLUORESCENT DISCHARGE LAMP Takizo Kobayashi, Kawanishi City, Japan, assignor to Keiji Tanaka, Nara-City, Japan Application April 17, 1957, Serial No. 653,461 6 Claims. (Cl. 315-100) This invention relates to a flash (high output) lighting operating circuit for a fluorescent discharge lamp. 7

An object of this invention is to provide a flash or high output lighting operating circuit for a fluorescent discharge l-amp which will not influence the life of the lamp even though an excessive lamp current is passed.

With the recent development of fluorescent discharge lamps, various attempts to use them by adjusting the light of the new light sources have been made and have come to be widely practised. However, no attempt has ever been made to use them by flashing the light sources. The present invention is to develop a new field of use of fluorescent discharge lamps by providing operating circuits effective to flash them.

There are two important problems to be considered in flashing fluorescent discharge lamps. The first of them is a problem of the extreme reduction of the life of the lamp as caused by the flash. The second is a problem of the reduction of the efliciency of the lamp by the saturating characteristic of the fluorescent material due to the excessive lamp current. However, the latter of the problems has been remarkably improved by the recent great progress in the technique of producing fluorescent materials. In view of the fact that high output lamps having a high efflciency taking a lamp current of more than 1 ampere in a 38 mm. tube have already appeared in the United States of America, this latter problem is thought to be able to be easily solved. Therefore, to make the flash of fluorescent discharge lamps possible is to solve the first problem. The present invention is to provide a lighting circuit which will not influence the life of lamps in flashing.

First of all, the fundamental operating principle of this invention shall be explained.

All of the causes of shortening the life of a fluorescent lamp by its flash are due to the evaporation of the oxide coating caused by the overheating of the arc spots by an excessive lamp current. Therefore, in order to eliminate the cause of shortening the life of the lamp due to flash, it is necessary to devise an operating circuit system wherein the arc spots of the electrodes will not be overheated by such excessive lamp current. The present invention relates to a very eflfective flash lighting operating circuit for a fluorescent discharge lamp wherein such requirement is attained by increasing the impedance of the cathode heating circuit.

The invention will be full explained in the following description made in connection with the accompanying drawings in which:

Fig. 1 is a fundamental circuit diagram for explaining the principle of operation according to this invention.

Fig. 2 is a circuit diagram showing an embodiment of the invention.

Fig. 3 is a circuit diagram showing another embodimerit of the invention.

Fig. 4 is a circuit diagram showing an embodiment of the invention as applied to a stepped light adjusting sys- 2 tom operating circuit including the flash lighting operation.

Fig. 5 is a circuit diagram similar to Fig. 4 but showing another embodiment of the invention.

The fundamental principle of the effect of preventing the overheating of the spot temperature by the action of eliminating the cathode preheating voltage due to the lamp shunt current produced by the increase of the impedance of the cathode heating circuit and by the action of dispersing the arc spots of the electrodes as purported by the present invention shall be explained with reference to Fig. 1.

The signs used in Fig. 1 and the specification represent the following:

i A lamp current.

ita, itb Respective lamp shunt currents flowing on sides a and b.

itbf A component which becomes a lamp current with the opposite filament end part, that is; the spot on the side was a base point through'the electrode filament among itb.

itbL A component which directly becomes a lamp current from the end part of the side b of the filament when the spot is dispersed by the operating efiect accompanying the increase of the impedance of such cathode heating circuit as is described later.

Here,

i =ita+itb, and

i =(zta-i-izbf)-l-.(itbL) The part (ita-Htbf) in this formula is a lamp current component flowing with the spot at the end part of the side a of the filament as a base point. 7 itbL is a lamp current component flowing with the spot at the end part of the side b of the filament as a base point.

B) An electric source circuit voltage of the cathode heating circuit.

E0 An electric source circuit voltage of the main discha ge circuit. Zf An outer series impedance element of the cathode heating circuit. I Z0 A stabilizing series impedance element of the main discharge circuit. rf A cathode filament resistance of the lamp. ih A cathode preheating current at the time of starting. Ia Acombined current on the side a. Ib Acombined current on the side b. Vfo A cathode heating voltage at the time of preheating the lamp.

Vfo=ih-rf if A cathode heating current during the lighting. if=ihitbf Vf A cathode heating voltage during the lighting.

' Vf=if-rf REMaRKs.-.By the efiect of the distributed current of the lamp current due to the increase of the impedance of the cathode heating circuit as described later, even in the constant normal cathode heating voltage type stabilizer system, the cathode heating voltage will be eliminated from Vfo at the time of preheating to V during the lighting.

0 A phase difference angle between the lamp current i and the cathode preheating current ih.

V- aa' A lamp voltage between a and a.

V bb' A lamp voltage between b and b.

The fundamental circuit diagram for explanation shown in Fig. 1 is of a normal constant cathode heating 3. voltage type filament transformer type stabilizer. The cathode preheating current and the cathode preheating voltage in this circuit will be as follows:

After the starting, as the series impedance element Zf, is inserted in the cathode heating circuit and the main discharge circuit source and the cathode heating circuit source are-connected in additive polarity, the respective lamp shunt currents ita and .itb of the lamp current 1T will be as follows:

Here, if the series impedance Z of the cathode heating circuit is selected to becomparatively high as compared with the cathode filament resistance r of the lamp, ita itb, ita -I- andalso Ia=1=ih.

Further, as the main discharge circuit source E0 and each cathode heating source E are connected in additive polarity, if .2) and Z0 are 'of the same polarity impedance, that is more correctly,-if the phase difference angle of .the lamp current b and the cathode heating current ih is less than 90 degrees, the spots of the lamp will naturally exist at the points a and a. In this case, in alternating current lighting, the operating mechanismywhen the'electrode filament acts as an anode will beditferent from :that when it acts as a cathode. It may bethought that the distributed current characteristics of the lamp current must be considered separately from the respective anode and cathode. However, when the wave forms of the respective currents Ia and lb are photographed with an oscillograph, the positive half cycle and the negative half cycle will be-exactly symmetrical. Therefore, practically it is not necessary to separately consider the respective operations -as'of the anode and-cathodeof the electrode every half cycle. That is to say, Ia, Ib-and ita, itb are of perfectly symmetrical wave forms. Therefore, if the circuit constant of ita on the side a is'equal to that of ita' on the side-d of the opposite electrode of the lamp in the half cycle of an alternating-current, ita=ita' and likewise itb=itb',Ia=Ia"and-Ib=Ib'.

Now, the action-of-eliminating the-cathode preheating voltage and the action of dispersing the arc spots by the lamp shunt current as purported by the present invention shall be detailed in the following:

(i) In case 0:0, that is, when i and ih are of ,the same phase: Ia and Ib in the Formula '5 will be a mere algebraic sum or difference of ita and itb with ih. Therefore, as the cathode heating current during lighting is if=ihitb, it will also=naturally become an algebraic difference.

Here, if the circuit constant is selected so that ih=itb, then if=0. The cathodeheating voltage Vf during the lighting will be 'Vf=if-rf=0 and will be-completely eliminated by the eliminating action of the lamp shunt current itb.

If itb is selected so that itb ih, not only Vf=0 but also the spots will be dispersed and will come to be present not-only on the sides a and a of the lamp :but

also on the sides b and b' thereof. In such case,the

'lampshunt .currentitb willabe'dividedinto itb anditbL V- aa' between a and 11' equal to the lamp voltage V bb' between b and b. The lamp shunt current itbL (itbL=itbitbf) obtained by removing itbf from itb will all become a lamp current component having as a base point the spot newly produced on the side b.

(II) In case 0 0 i90z When the phase difference angle 0 between the lamp current i and the cathode preheating current-ih has any angle within 190 degrees, they will have the values of the critical lamp shunt current and the smallest cathode heating voltage represented by the general formulas itb=ih cos 0 (6) Vf=Vf0 sin 0 That is to say, in other words, in case i and ih are not of the same phase but have an angle 0 less than degrees, Vf will not be eliminated below Vfo sin 0. This is the critical value of the elimination of the cathode preheating voltage by the lamp shunt current. The critical lamp shunt current itb will be ih cos 0 at this time as in the Formula 6 and will be itb in case the critical lamp shunt current ih cos Oitb. At this critical lamp shunt current itbf, the lamp voltage V aa between a and a and the lamp voltage V- -bb between b and b will become equal even if Vf is not eliminated to 0 volt.

The lamp shunt current itb will be divided into the part of itbf=ih cos 0 and itbL. The former itbf will become a lamp current component having the spot on the side a as a base point together with iza. Excessive itbL (itbL=itbitbf) will become a lamp current component having as a base point the spot newly formed on the side b.

(Iii) In case 0 i90z When the phase difference angle between i and ill is more than 90 degrees, that is, when Zf and Z0 are formed of reactance elements heterogeneous to each other, the phase difference angle will be more than 90 degrees.

In such case, the spots will turn to the sides b and b and will be present there. That is to say, it is because, even though the lamp voltage V aa' between a and a is higher than V bb at the time of starting the lamp when the cathode is preheated, they will be reversed and V aa' will be lower than V bb' after lighting. In such case that 0 -90, when the cathode heating circuit source and the main discharge circuit source are connected in subtractive polarity or in additive polarity, it will be necessary to transfer the inserting place of Z to the side b, that is, such circuit connections as are shown in Figs.2 and 3 will be made.

Thus, unless the connection is changed, the significance of the increase of the impedance of the cathode heating circuit will be lost.

The above is the summarized explanation of the action of eliminating the cathode preheating voltage and the action of dispersing the spots on the basis of the increase of the impedance of the cathode heating circuit.

The present invention is to provide a flash operating 'circuitfor a fluorescent discharge lamp which will not .whichis a lighting circuit made to perform the three operations of fiash lighting, rated lighting and dimmedlight- .ing by means of a switch with one fluorescent lamp.

In Fig. 4, 1 is a primary coil, 2 is.a secondary coil -(which may be omitted in case the circuit is to bezused for afluorescent lamp adapted torthe feederlinesource) and '3 and 4 are cathode heating coils which are the cathode heating coils themselves of Fig. 1 with Z removed as the impedance has been increased by means of a leakage transformer relating to the cathode heating coils with magnetic short-circuits provided between the primary coil 1 and them. The type of the stabilizer is of the normal constant cathode heating Voltage system. However, it is a new circuit system for eliminating the cathode preheating voltage by effectively applying the action of eliminating the cathode preheating voltage by means of the distributed current of the lamp current and also the action of dispersing the spots to be added thereto. Now, the operation of said circuit shall be explained.

First of all, if an electric source switch 8 is closed in the state wherein a light adjusting switch 7 is placed at a point I, the respective cathodes of the fluorescent discharge lamp 9 will be preheated by the cathode heating coils 3 and 4 and then started, that is, will have the process of the so-called immediate lighting. While the light adjusting switch 7 is placed at the point I, chokes 5 and 6 for stabilizing the main discharge circuit will be connected in series, the lamp current will be thereby limited to a low value and the lamp will be placed in a dimmed lighting state.

Now, when the light adjusting switch 7 is turned to a point 11, the stabilizing choke 6 will be short-circuited and the lamp designed so as to be limited to a rated lamp current by the impedance of only the stabilizing choke 5 will be placed in the rated lighting state. Further, if the light adjusting switch 7 is turned to a point III, said series chokes 5 and 6 will be connected in parallel, the impedance value of the circuit will decrease, the lamp current will increase and the lamp will-be placed in a flash lighting state.

In the respective steps of adjusted lighting including the flash, though the lamp current changes greatly, the spots of the filament wvill be always kept at a constant proper temperature and will not be overheated. This is because the cathode heating coils 3 and 4 of this circuit has had the impedance increased and the lamp current iand the cathode heating current ih are in almost the same phase, that is, the circuit constant is selected in the condition of :0. Further, as the impedance value of the series choke for stabilizing the discharge circuit is made variable by the light adjusting switch 7, the discharge circuit voltage will be constant. Therefore, as the lamp voltage will not change in the whole range of light adjustment, the phase angle of the lamp current will be constant. The phase angle of ih will be also constant and therefore 0 will be constant over the whole range of light adjustment and will keep the condition of 0: 0. Therefore, the action of eliminating the cathode preheating voltage by the lamp shunt current and the action of dispersing the spots will operate very efiectively. That is to say, in the stage wherein the lamp current at the time of dimmed lighting is low, the lamp shunt current will be small, therefore the action of eliminating the cathode preheating voltage will be low and, because itb ih cos 0, there will be no effect of dispersing the spots.

Due to the increase of the lamp shunt current in the rated lighting state (when the light adjusting switch 7 is at the point 11), the cathode preheating voltage will be almost eliminated. Now, in the flash lighting state, the lamp shunt current will remarkably increase, the cathode preheating voltage will be almost completely eliminated, the spot will be dispersed into two and will endure the flash lamp current about twice as large as the lamp current and the temperature of the spot will neither rise nor influence the life of the lamp.

Fig. shows a modified circuit for the stepped adjusted lighting system including the above mentioned flash lighting in the case that the series impedance element 23 of the cathode heating circuit is by the outer reactance element.

As detailed in the above, the present invention is a fundamental invention aiming atperforming the action of eliminating the cathode preheating voltage and the.

6 action of dispersing the spots by the lamp shunt current produced by increasing the impedance of the cathode heating circuit in a constant cathode heating voltage type stabilizer and is an invention wherein the flash lighting of a fluorescent discharge lamp and the adjustment of light are thereby made possible.

What I claim is:

1. An operating system for a fluorescent discharge lamp of the type having a pair of filaments, comprising a main supply circuit including a source of voltage and a stabilizing impedance, and a heating circuit connected to each filament and including a source of filament heating voltage and a heating circuit impedance, said main supply circuit being connected between said filaments, the value of each said heating circuit impedances being high compared to the value of the impedance of each filament itself, whereby over-heating of the filaments by excessive lamp current is prevented.

2. The invention of claim 1, wherein the impedances in said heating circuits and said stabilizing impedance are all inductances.

3. The invention of claim 1, said source of supply voltage comprising a transformer, said sources of heating voltage comprising windings of said transformer, said heating circuit impedances comprising leakage reactance in said transformer.

4. The invention of claim 1, said stabilizing impedance having two parts, and means including a multiple position switch for short-circuiting one of said parts, for connecting said parts in series, or for connecting said parts in parallel, selectively.

5. An operating system for a fluorescent discharge lamp of the type having a pair of filaments, comprising a main discharge circuit including a source of voltage and a discharge stabilizing impedance connected between the filaments, a cathode heating circuit connected to each filament including a source of filament heating voltage and a heating circuit impedance, the phase difference angle between the lamp current and the cathode heating current being within the range from 0 to :90, the cathode heating circuits and the main discharge circuit being connected in additive polarity, each said heating circuit impedance being inserted in its heating circuit at a point nearer to the filament terminal at which the voltage is higher than the other terminal when the lamp is lighted and having a value such that when the lamp is lighted two are spots are produced on eachfilament and the lamp can withstand an excessive lamp current which is up to about 200% of the standard current.

6. An operating system for a fluorescent discharge lamp of the type having a pair of filaments, comprising a main discharge circuit including a source of voltage and a discharge stabilizing impedance connected between the filaments, a cathode heating circuit connected to each filament including a source of filament heating voltage and a heating circuit impedance, the phase difference angle between the lamp current and the cathode heating current being within the range from +90" to +l or to the cathode heating circuits and the main discharge circuit being connected, each said heating circuit impedance being inserted in its cathode heating circuit at a point nearer to the filament terminal at which the voltage is lower than the other terminal when the lamp is lighted and having a value such that when the lamp is lighted two are spots are produced on each filament and the lamp can withstand an excessive lamp current which is up to about 200% of the standard current.

References Cited in the file of this patent UNITED STATES PATENTS 2,802,143 Kobayashi Aug. 6, 1957 2,824,263 Strecker et aL'--- Feb. 18, 1958 2,829,314 Vradenburgh Apr. 1, 1958 

